William Stallings Computer Organization and Architecture file`CD-ROM `CD-Writable (WORM) `CD-R/W...
Transcript of William Stallings Computer Organization and Architecture file`CD-ROM `CD-Writable (WORM) `CD-R/W...
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William Stallings Computer Organization and ArchitectureChapter 5Memori External
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Jenis Memori External
Magnetic DiskRAIDRemovable
OpticalCD-ROMCD-Writable (WORM)CD-R/WDVD
Magnetic Tape
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Magnetic Disk
Metal atau plastic dilapisi dg material yg bersifat magnet (iron oxide)Jenis kemasan
FloppyWinchester hard diskRemovable hard disk
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Format dan Organisasi Data
Lingkaran konsentris atau trackAda Gap antar trackGap sempit, kapasitas bertambahJumlah bit per track sama (kerapatan bervariasi)Kecepatan putar tetap
Track dibagi menjadi beberapa sectorUkuran minimum block adalah satu sectorSatu block bisa berisi lebih dari satu sector
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Fixed/Movable Head Disk
Fixed headAda satu head (r/w) per trackHead diletakkan pada tangkai yg tetap
Movable headHanya ada satu head per sideDiletakkan pada tangkai yg dpt bergerak
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Removable / Nonremovable
Removable diskDapat dilepas dari drive dan diganti dg disk lain Memberikan kapasitas simpanan yg tak terbatasMudah melakukan transfer data antar sistem
Nonremovable diskTerpasanang permanen dalam drive
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Floppy Disk
8”, 5.25”, 3.5”Kapasitas kecil
sampai 1.44Mbyte (ada yg 2.88M)
LambatUmum dipakaiMurah
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Winchester Hard Disk (1)
Dikembangkan oleh IBM di Winchester (USA)Dikemas dalam satu unitBerisi satu cakram atau lebihHead sangat kecilHandal
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Winchester Hard Disk (2)
Umum digunakanMurahSbg external storage yg sangat cepatKapasitas semakin besar
Dalam orde GB
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Removable Hard Disk
ZIPMurahBanyak digunakan100MB
JAZMahal1G
L-120 (a: drive)Juga dpt untuk membaca 3.5” floppy
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Pencarian Sector
Harus dapat mengenali awal suatu track dan sectorFormat disk
Menambahkan informasi tambahanMemberi tanda awal track dan sector
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Gap1 Id Gap2 Data Gap3 Gap1 Id Gap2 Data Gap3
TrackSyncByte Head Sector CRC Sync
ByteData CRC
ST506 format (old!)
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Karakteristik
Fixed head atau movable headRemovable disk atau fixed diskSingle side atau double sideSingle platter atau multiple platterMekanisme head
Contact (Floppy)Fixed gapFlying (Winchester)
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Multiple Platter
Satu head per sideSemua head di-join dan di-alignTrack-track yg setiap platter membentuk cylinderData dipecah berdasarkan cylinder
Mengurangi gerakan headMeningkatkan kecepatan (transfer rate)
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Kecepatan
Seek timegerakan head ke track yg dituju
(Rotational) latencyPutar platter sampai posisi data dibawah head
Access time = Seek + LatencyTransfer rate
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RAID
Redundant Array of Independent Disks Redundant Array of Inexpensive DisksAda 6 level Tidak berhirarkiSejumlah disks (fisik) yg dipandang sbg satu drive (logical) oleh Sistem OperasiData tersebar diantara disk fisik
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RAID 0
No redundancyData striped across all disksRound Robin stripingIncrease speed
Multiple data requests probably not on same diskDisks seek in parallelA set of data is likely to be striped across multiple disks
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RAID 1Mirrored DisksData is striped across disks2 copies of each stripe on separate disksRead from eitherWrite to bothRecovery is simple
Swap faulty disk & re-mirrorNo down time
Expensive
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RAID 2
Disks are synchronizedVery small stripes
Often single byte/word
Error correction calculated across corresponding bits on disksMultiple parity disks store Hamming code error correction in corresponding positionsLots of redundancy
ExpensiveNot used
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RAID 3
Similar to RAID 2Only one redundant disk, no matter how large the arraySimple parity bit for each set of corresponding bitsData on failed drive can be reconstructed from surviving data and parity infoVery high transfer rates
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RAID 4
Each disk operates independentlyGood for high I/O request rateLarge stripesBit by bit parity calculated across stripes on each diskParity stored on parity disk
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RAID 5
Like RAID 4Parity striped across all disksRound robin allocation for parity stripeAvoids RAID 4 bottleneck at parity diskCommonly used in network servers
N.B. DOES NOT MEAN 5 DISKS!!!!!
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Optical Storage CD-ROM
Originally for audio650Mbytes giving over 70 minutes audioPolycarbonate coated with highly reflective coat, usually aluminumData stored as pitsRead by reflecting laserConstant packing densityConstant linear velocity
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CD-ROM Drive Speeds
Audio is single speedConstant linier velocity1.2 ms-1
Track (spiral) is 5.27km longGives 4391 seconds = 73.2 minutes
Other speeds are quoted as multiplese.g. 24xThe quoted figure is the maximum the drive can achieve
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00 00FF x 10 M
inSe
cSe
ctor
Mod
e
DataLayeredECC
12 byteSync
4 byteId
2048 byte 288 byte
2352 byte
CD-ROM Format
Mode 0=blank data fieldMode 1=2048 byte data+error correctionMode 2=2336 byte data
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Random Access on CD-ROM
DifficultMove head to rough positionSet correct speedRead addressAdjust to required location(Yawn!)
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CD-ROM for & against
Large capacity (?)Easy to mass produceRemovableRobust
Expensive for small runsSlowRead only
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Other Optical Storage
CD-WritableWORMNow affordableCompatible with CD-ROM drives
CD-RWErasableGetting cheaperMostly CD-ROM drive compatible
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DVD - what’s in a name?
Digital Video DiskUsed to indicate a player for movies⌧Only plays video disks
Digital Versatile DiskUsed to indicate a computer drive⌧Will read computer disks and play video disks
Dogs Veritable DinnerOfficially - nothing!!!
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DVD - technology
Multi-layerVery high capacity (4.7G per layer)Full length movie on single disk
Using MPEG compression
Finally standardized (honest!)Movies carry regional codingPlayers only play correct region filmsCan be “fixed”
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DVD - Writable
Loads of trouble with standardsFirst generation DVD drives may not read first generation DVD-W disksFirst generation DVD drives may not read CD-RW disksWait for it to settle down before buying!
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Foreground Reading
Check out optical disk storage optionsCheck out Mini Disk
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Magnetic Tape
Serial accessSlowVery cheapBackup and archive
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Digital Audio Tape (DAT)
Uses rotating head (like video)High capacity on small tape
4Gbyte uncompressed8Gbyte compressed
Backup of PC/network servers